The present invention relates to a semiconductor device and a fabrication method for the same, and more particularly to a semiconductor device having bit lines and word lines intersecting with the bit lines and a fabrication method for such a semiconductor device.
The structure of a semiconductor device having bit lines and word lines orthogonal to the bit lines is outstanding for the capability of reducing the memory cell area, and is essential for miniaturization of the semiconductor device. To attain desired properties with such a structure, the impurity profile must be made proper.
For formation of a semiconductor device having bit lines and word lines intersecting with the bit lines, a method as follows, for example, is disclosed (see Japanese Laid-Open Patent Publication No. 2001-077220, for example).
First, on a semiconductor substrate of a first conductivity type, formed is an ONO film composed of a lower oxide film, a nitride film and an upper oxide film sequentially placed one upon another. Part of the ONO film is then removed in stripes using a mask pattern. Subsequently, an impurity of a second conductivity type is implanted in the portions of the semiconductor substrate of the first conductivity type from which the ONO film has been removed, to form bit lines. After removal of the mask pattern, insulating films are formed on the bit lines. A conductive material is then deposited, and the deposited conductive material is selectively removed, to form word lines in a direction orthogonal to the direction in which the bit lines extend.